The present invention relates to a method for producing a creped nonwoven fibrous web.
Creping is a process in which a nonwoven fibrous web is adhered to a surface of a roll or drum using an adhesive and the adhered nonwoven web is mechanically removed from the surface of the roll or drum. This mechanical removing of the adhered nonwoven web debonds and disrupts the fibers within the nonwoven web, thereby increasing the absorbency, if absorbent fibers are used, softness, and bulk of the nonwoven web. Creping has also been used in the paper making art.
Traditionally in creping processes, adhesives have been used to attach a pre-bonded nonwoven fibrous web to a creping roll. Typically, water-based adhesives, such as latex adhesives, have been used to attach a nonwoven fibrous web to a creping roll or creping drum. In the prior processes used in the art, the fibers of the nonwoven web are bonded together, in a separate bonding step, before the nonwoven web is adhered to the creping roll.
Preparation of creped nonwoven webs is known in the art, for example, see U.S. Pat. No. 3,665,921, U.S. Pat. No. 3,668,054, U.S. Pat. No. 3,687,754, U.S. Pat. No. 3,694,867, U.S. Pat. No. 3,705,063, and U.S. Pat. No. 3,705,065, all issued to Stumpf, and hereby incorporated by reference in their entirety. In each of the above-mentioned patents to Stumpf, a high loft nonwoven web having a multiplicity of looped fibers is produced. The Stumpf patents do not teach bonding the nonwoven web while the nonwoven web is on the creping roll or drum.
U.S. Pat. No. 4,810,556, issued to Kobayashi et al. discloses a process of producing a creped nonwoven web by coating an uncreped nonwoven fabric with a lubricant and then pressing the nonwoven fabric between a drive roll and a plate having a rough surface. The plate is positioned near the drum and is substantially parallel or tangential to the outer surface of the drum. The nonwoven web is crinkled in a wavelike fashion in the direction of movement by the frictional force caused by the pressing. The resulting nonwoven web is creped, which contributes to the softness of the nonwoven web.
In addition, the preparation of creped thermoplastic nonwoven webs is described in WO 99/22619, and U.S. Pat. No. 6,197,404 issued to Verona, both assigned to Kimberly-Clark Worldwide, Inc and hereby incorporated by reference in their entirety. The creped nonwoven web of WO ""619 and U.S. ""404 has a permanent crepe, wherein regions of interfilament bonding, which are permanently bent out-of-plane, are alternated with regions of no interfilament bonding. In the process disclosed in WO ""619 and U.S. ""404, a doctor blade is used to crepe the nonwoven fabric from the creping roll. The nonwoven web is supplied to the creping roll from a roll of pre-bonded, uncreped nonwoven web.
Therefore, there is a need in the art for a process of bonding and creping a nonwoven web in a single step process which can be easily added to the nonwoven web formation process.
The present invention provides an improved method of producing creped nonwoven fibrous webs derived from thermoplastic polymers. The process of the present invention provides an effective method of bonding and creping thermoplastic nonwoven webs in the nonwoven web production line.
The method of the present invention prepares a pattern bonded and creped nonwoven web wherein the method comprises
a) providing a nonwoven fibrous web having a first side and a second side, the nonwoven fibrous web comprises thermoplastic fibers;
b) transferring and adhering the nonwoven fibrous web to a first roll, such that the first side of the nonwoven fibrous web faces the first roll;
c) bonding the nonwoven fibrous web transferred and adhered to the first roll by contacting the nonwoven fibrous web with a second roll comprising a pattern, such that the nonwoven fibrous web is passed between a nip formed between the first roll and the second roll to form a bonded nonwoven web; and
d) removing the bonded nonwoven web from the first roll by creping the bonded nonwoven web from the first roll to produce a creped nonwoven web.
In a second method of the present invention, both sides of the nonwoven web can be creped. When both sides of the nonwoven web are creped, the process described above further comprises
e) transferring and adhering the second side of the nonwoven web to a third roll by contacting the second side of the nonwoven fibrous web with the third roll; and
f) removing the nonwoven fibrous web adhered to the third roll by creping the nonwoven fibrous web from the third roll with a creping blade to produce a creped thermoplastic nonwoven web which is creped on both the first and second sides.